A major deficiency of compression molded thermoset glass fiber reinforced polyester (FRP) moldings is surface imperfections such as pits, pores, surface cracks, waviness and sink marks. The in-mold coating process of U.S. Pat. No. 4,081,578 generally overcomes these imperfections by molding a low viscosity thermoset on top of the FRP in a second molding operation. The composition described in U.S. Pat. No. 4,081,578 contains free hydroxyl as well as isocyanate groups that co-react at room temperature, resulting in a limited (about one-half hour) pot life. In practice, the reactive ingredients are kept apart, and combined only immediately prior to application. This necessitates dual pumping equipment and an accurate metering device, which increase the cost and complexity of the system. A single component coating would thus offer a significant advantage. Moreover, conductive carbon black does not dispense well in isocyanate based in-mold coating compositions, and it is difficult to obtain after in-mold coating and subsequent electrostatic painting, a paint layer which is even.
Therefore, it is an object of this invention to avoid the difficulties alluded to and to provide a process for in-mold coating an FRP molding with a one-component coating composition.
Another object of this invention is to provide a composition suitable for in-mold coating an FRP molding.
A further object of this invention is to provide a cured molded FRP molding or part with an adherent coating in-mold coated with a one component in-mold coating composition.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and working examples.